The present invention relates broadly to an electromagnetic interference (EMD shielded or grounded panel assembly including a porous, electrically-conductive shielding media and an electrically-conductive frame for supporting the media, and more particularly to such an assembly which is adapted to cover a corresponding ventilation opening in an electronics housing or other enclosure enclosures and which accommodates the flow of cooling air into the enclosure while maintaining electrical continuity and EMI shielding effectiveness across the opening.
The operation of electronic devices such as televisions, radios, computers, medical instruments, business machines, communications equipment, and the like is attended by the generation of electromagnetic radiation within the electronic circuitry of the equipment. As is detailed in U.S. Pat. Nos. 5,202,536; 5,142,101; 5,105,056; 5,028,739; 4,952,448; and 4,857,668, such radiation often develops as a field or as transients within the radio frequency band of the electromagnetic spectrum, i.e., between about 10 KHz and 10 GHz, and is termed "electromagnetic interference" or "EMI" as being known to interfere with the operation of other proximate electronic devices.
For attenuating EMI effects, shielding having the capability of absorbing and/or reflecting EMI energy may be employed both to confine the EMI energy within a source device, and to insulate that device or other "target" devices from other source devices. Such shielding is provided as a barrier which is interposed between the source and the other devices, and most often is configured as an electrically conductive and grounded housing or other enclosure, such as a room, which surrounds the EMI generating circuitry of the source device. However, when such circuitry is contained within the confined space of an enclosure, it often is necessary to provide a cooling or ventilation means to dissipate the heat which is ohmicly or otherwise generated by the circuitry. Most enclosures therefore are formed with one or more air intake and/or exhaust openings or ports for natural or forced convective circulation of air between the interior of the enclosure and the ambient environment.
Left uncovered, such openings would represent a discontinuity in the surface and ground conductivity of the enclosure, with the result of a decrease in the EMI shielding effectiveness of the enclosure. Accordingly, shielded vent panels have been proposed for covering the openings in an manner which allows for the ventilation of the enclosure while electrical continuity, i.e., grounding, across the vent opening is maintained. In basic construction, such vent panels, which are sized to span the corresponding opening in the enclosure, conventionally are formed as including a sheet of a porous, electrically conductive shielding media, and an electrically-conductive frame member configured to support the media as extending about the outer periphery thereof. The media, which may be an expanded metal mesh or, alternatively, a honeycombed-structured or other cellular structured metal foil, is received in or otherwise is attached to the frame, which typically is provided as an extruded aluminum or other metal profile. The frame, in turn, may be fastened to the enclosure over the opening thereof with screws or the like, with a compressible, electrically-conductive seal or gasket optionally provided for improved electrical contact between the frame and the enclosure.
However, for electrical continuity to be maintained across the opening, good electrical contact must be provided not only as between the frame and the enclosure, but also as between the media and the frame. In this regard, conventional panels may employ a C-shaped frame channel including a V-shaped or other projection integrally formed within one of the sides of the channel. With the peripheral edges of the media being received within the channel, the sides thereof are compressed to cause the projection to penetrate into the media and thereby establish good electrical contact. Vent panels of such type are marketed commercially by the Chomerics Division of Parker-Hannifin Corp. (Woburn, Mass. under the tradenames "Cho-Cell.TM.," "Shield Cell.RTM.," and "Omni Cell.RTM.s." Alternatively, the media may be fit into the frame and then bonded thereto using a conventional joining technique such as resistance welding, brazing, soldering, or the like.
Another method of attaching the media to the frame involves using the gasket typically provided between the frame and the enclosure to hold the filter media in place. As is described in commonly-assigned U.S. Pat. No. 5,032,689, the frame in such method may be integrally-formed as including a ridge over which the gasket is press-fitted for its retention about the periphery of the frame. The gasket, in turn, may be configured to overlap the media for securing the media to the frame.
U.S. Pat. No. 3,580,981 discloses another shielding vent panel wherein an electrically conductive textile is positioned about the periphery of the media for contact between the media and the frame which may have an L-shaped or generally Z-shaped profile. To assure good conductivity, the frame, media, and textile are covered with an electrically-conductive coating or plating such as by immersion in a molten tin or metal bath. Other vents and materials therefor are described in U.S. Pat. Nos. 3,546,359; 3,553,343; 3,584,134; 3,821,463; and 4,616,101.
In view of the continued proliferation of electronic devices, it is to be expected that continued improvements in EMI shielded vent panels would be well-received by industry, and particularly by semi-conductor manufacturers for use in the processing of silicon wafers and the like. A preferred seal construction would be economical to manufacture, but also would exhibit reliable shielding performance in assuring good electrical contact between the shielding media and the frame member.